iam working in 8051 microcontroller i want to know about the dynamic memory allocation in Keil c just operation of memset
memset() has nothing to do with dynamic memory allocation, but if you want to know about memset(), the manual wouldn't be a bad place to start:
http://www.keil.com/support/man/docs/c51/c51_memset.htm
Your favorite C textbook likely mentions memset() too.
Oh well, both original links worked from the preview, but after posting the link gets prefixed with some extra keil.com/forum/docs/ URL stuff and gets quoted.
Just copy the link from your browser and paste it into the browsers URL/Address text box.